The present invention relates to secure transmission between a system and at least one user having a terminal.
It is very common to cipher transmission, so that only allowed receiving users, who have a specific key, can decipher the transmitted data.
Such ciphering can take place for instance, but of course not exclusively, in a broadcasting system, such as a DVB (Digital Video Broadcasting) network. The DVB system, and more particularly its DVB-H version adapted to handheld terminals, is fully described in the European standard EN 302 304, V1.1.1, “DVB (Digital Video Broadcasting); Transmission System for Handheld Terminals (DVB-H)”, published by the ETSI (European Telecommunications Standards Institute) in November 2004.
FIG. 1 illustrates a DVB-H system in which a transmitter 1 multiplexes, through MUX 3, a plurality of streams s1, s2, . . . , sn, which can concern different services, e.g. a video service, a data service, an audio service, etc. Before being transmitted over a radio broadcasting channel 6 from an antenna 5, the resulting signal is multiplied by a ciphering key Kc (see multiplier 4).
A receiver 2 incorporated in a handheld terminal and listening to the channel 6 can get the ciphered signal through its antenna 7. If the user of the terminal is allowed to receive the services, he must have a deciphering key Kd capable of deciphering the signal. Such deciphering key can be a key dual to Kc, and can be public or private as well known by one skilled in the art. The signal resulting from the multiplication between the received signal and Kd (see multiplier 8) is finally demultiplexed by DEMUX 9 in order to obtain streams r1, r2, . . . , rn substantially corresponding to the streams broadcasted by the transmitter 1. Further detail of the operations hold in transmitter 1 or receiver 2 is in conformity with the above-mentioned European standard EN 302 304.
Of course, ciphering can apply to all the streams as in FIG. 1, but it can also apply to some of the streams only. This can happen e.g. when the different streams correspond to different broadcasted TV channels, some of which are with charge for admission. In this case, only the users having a subscription for these channels should be provided with the corresponding deciphering key.
An easy way of providing the subscribers with deciphering key Kd is to send them a key K equal to Kd or from which Kd can be derived. However, when transmitting such key K over a radio channel, there is a risk that a hacker can listen to the transmission channel and intercept the key and then have access to the service without having a subscription.
In other respects, hybrid systems including a broadcasting subsystem and a radiocommunication subsystem are developing. For example, there are currently some efforts to propose hybrid systems combining a DVB subsystem and a cellular interactive communication subsystem, e.g. a GSM (Global System for Mobile communications), GPRS (General Packet Radio Service) or UMTS (Universal Mobile Telecommunication System) subsystem.
Such systems are of great interest because both subsystems have complementary advantages: DVB can transmit identical data to a large number of users with high data rates, whereas GSM or UMTS provides a return channel making the transmission interactive. Some terminals can be equipped to operate with both subsystems.
Although the hybrid systems offer improved services compared to the separate subsystems, such as video on demand or e-commerce applications, they do not resolve the above-mentioned problem, since the key used for deciphering the information sent from the DVB subsystem for instance is still transmitted over a radio channel which could be spied by hackers. Therefore, in hybrid systems, transmission of information is still subject to attacks.
An object of the present invention is to secure transmission in a hybrid system.
Another object of the invention is to limit the access to certain services to allowed users only in a hybrid system.
Another object of the invention is to limit the access to certain services to some areas only in a hybrid system.